The use of liquid carbon dioxide for producing CO.sub.2 snow and subsequently accelerating it to high speed for cleaning particles from a substrate is taught by Layden in U.S. Pat. No. 4,962,891. A saturated CO.sub.2 liquid having an entropy below 135 BTU per pound is passed through a nozzle for creating, through adiabatic expansion, a mix of gas and CO.sub.2 snow. A series of chambers and plates are used to enhance the formation of larger droplets of liquid CO.sub.2 that are then converted through adiabatic expansion into solid CO.sub.2 snow.
My U.S. Pat. No. 5,405,283 was directed to an apparatus for creating CO.sub.2 snow which utilizes inexpensive components and readily available low pressure shop air for improving the efficiency of creating CO.sub.2 snow and for improving the coagulation of the CO.sub.2 snow into larger CO.sub.2 particles. In this patent, a nozzle is provided for receiving and expelling liquid CO.sub.2 through an orifice sized for converting the liquid into CO.sub.2 snow. A body, defining a cavity therein, is coupled to the nozzle such that the snow is injected into the cavity. An exhaust nozzle is coupled to the body and the cavity therein for directing the pressurized CO.sub.2 snow toward the workpiece to be cleaned. In one variation, a mixing device is optionally coupled to the nozzle for receiving and mixing pressurized shop air and liquid nitrogen, and then directing the cooled shop air into the cavity for cooling the area adjacent to the nozzle. In this manner, the pre-cooled shop air enhances the efficiency of the conversion of liquid CO.sub.2 into CO.sub.2 snow particles by cooling and pressurizing the area adjacent to the orifices in the nozzle within the cavity.
A problem with this design is that the system sometimes experiences pulsing because vapor is trapped within the liquid CO.sub.2, which causes undesirable discontinuities in the formation of CO.sub.2 snow.